Large rotary fans are commonly used to circulate air within these houses and can be mounted within a wall thereof to circulate fresh air into or out of the house or hung out in the house to just circulate the air. Such fans include a wooden or metallic peripheral wall disposed about the fan's blades and motor in substantially coaxial relation to the axis about which the blades are rotated. The peripheral wall extends axially beyond the blades and motor, which are mounted internally of the wall by a frame connected thereto. One or more flanges extend from forward and rearward margins of the peripheral wall in substantial perpendicular relation thereto toward the aforesaid axis. Screens are connected to the flanges to prevent inadvertent insertion of foreign objects into the path of the fan blades.
The screens are constructed of perpendicular interconnected wire strands and further include one or more peripheral strands defining the lateral margin of the screen. The screens are typically mounted to the fan housing using plastic or wire ties which suspend the screens from the flanges. Alternatively, screws, having members attached thereto for engaging the peripheral strands, are threadably secured to the flanges to support the screen adjacent thereto. The problem with these methods of mounting the screens is that no tension is applied to the screen. As a result, the screens will eventually warp, becoming generally unattractive and, more importantly, may deflect and possibly become entangled with the fan blades if struck by an object. Most fans have brace members connected to the peripheral wall and extending adjacent the screen to prevent a warped screen from becoming entangled. Further, the screws and ties commonly used to secure the screens frequently disengage from the screen or flanges. The loss of the ties or screws diminishes the screen's effectiveness and could eventually result in the screen falling from the fan or becoming entangled therein.
Screens have been developed wherein the wire is tensioned and integrally connected to a peripheral frame prior to connecting the frame to the flanges. The process of connecting the wire to the frame is relatively complex as the frame is folded over the peripheral strands and stamped in close securing engagement therewith while the wire is held in tension by other apparatus. The machinery and labor necessary to perform this procedure are relatively expensive. Though the screen is tensioned, the cost of manufacture precludes the practical use of such screens for use on fans for livestock houses. Further, the frame is attached to the flanges using screws or ties and is susceptible to the shortcomings set forth above. Note that the tension in the framed screen is preset and cannot be adjusted. If the screen should lose tension, no apparatus and method are available to retension the strands.